MAGNETIC-FIELDS IN QUIESCENT PROMINENCES

We consider the formation of coronal magnetic structures associated with high-latitude solar prominences. Recent measurements of prominence magnetic fields using the Hanle effect indicate that the transverse fields in these prominences have inverse polarity, consistent with the Kuperus-Raadu model. However, the observed axial fields are inconsistent in sign with models in which the axial component is produced by differential rotation acting on a line-tied, coronal magnetic field overlying an east-west neutral line. We demonstrate that such an inverse axial field is generated when either (1) the neutral line in the initial unsheared state is nearly parallel to the solar meridian or (2) the axial field is produced by differential rotation acting on a transverse field below the solar photosphere. In the latter case the axial field emerges through the surface in the form of small bipoles with preferred orientation, and the elements of these bipoles move apart and interact with surrounding magnetic fields. The interaction involves reconnection and flux cancellation at the photosphere. As a result the axial field below the photosphere is transferred to a helical field in the corona. The prominence consists of cool plasma located at the lowest points of helical field lines. It is shown that the prominence field in this model has the correct transverse and axial components.